Off-grid solar charge controllers

[cedric]

Ok you have roughly 240 watt panels. Best configuration for an RV would be to wire them in series and minimum MPPT charge controller size is 40 amps @ 12 volt battery. A good quality product in that size is MorningStar Tri Star MPPT Controller

Thanks for the quick reply. Yes, they are 250watt mono panals from LG.
Could you help me understand why this is best? In series would be ~60volts input to the controller?Is that correct?

I was thinking connect the panels in parallel and use the SunSaver Duo. It is rated a 30v input

As you can tell I am in the first phase of the learning curve. thanks for the help

[Sunking]

I have two solar mono panels rated at 29.7 volts and 8.3 amps

I am using 12v batteries in my RV. Can you recommend a controller that would maximize my charging.
It's my understanding that only an mppt controller can down convert to 12v and make use of all the power by increasing the amps going into the batteries.
thanks for your help
cedric

Ok you have roughly 240 watt panels. Best configuration for an RV would be to wire them in series and minimum MPPT charge controller size is 40 amps @ 12 volt battery. A good quality product in that size is MorningStar Tri Star MPPT Controller

[cedric]

how do i figure the size charger needed

Here in Brisbane it rarely gets below 50deg F at night time in winter most of year its about 60 to 90F My other home in Philippines it never gets below 60 deg F on the coldest winters night.
My favourite PWM charger for small 12v systems is a Chinese copy of an old Steca model. No brand name but available here in Aus from a few big electronics stores.just about impossible to destroy it. Rated max input is 26v but it will take 36 v no problems and still never gets warm. Not like MPPT chargers that tend to die when operated 50% above rated input. They know they not that reliable as only 2 years warranty.. Another reason not good value most PWM as you know give 5 years, as they know there not going to be problem

Picture of it added its a 30a model

I have two solar mono panels rated at 29.7 volts and 8.3 amps

I am using 12v batteries in my RV. Can you recommend a controller that would maximize my charging.
It's my understanding that only an mppt controller can down convert to 12v and make use of all the power by increasing the amps going into the batteries.
thanks for your help
cedric

[Sunking]

I have decided to go with a 24 volt battery plan, my panels are 165 feet away from the controller

OK then that demands a Midnite Solar Classic 250 unit as it will allow you to run up to 274 Volts Voc panel voltage.

[paradiseisle]

Planing my Battery plan

I have decided to go with a 24 volt battery plan, my panels are 165 feet away from the controller and inverter and I know there will be a power loss with that long a run. I have yet to decide on a controller but am looking at the Outback Flex max 80 and a MidNight Solar Classic. Checking to see if they are over load or sufficient for what I need. Any info on what gauge wire to use on the 165 foot run would also be very helpful. A friend has 250 feet of 6 gauge he will sell me at a reduced price, but I don't want to buy it if it is not the right size.

[paradiseisle]

Yep it is, sorry.

Here is the deal. With a 80 amp MPPTcharge controller the max panel wattage is roughly

1000 watts @ 12 volts
2000 watts @ 24 volts
4000 watts @ 48 volts

You have 2450 watts.

OK with 2450 watts will produce roughly 50 amps of charge current. The minimum size Flooded Lead Acid battery you can run with 50 amps of charge current is 400 Amp Hours. So for a 6 volt battery you are looking at 8 batteries something like a Trojan LR16RE-B or a Rolls S-530 battery.

Ideal size is a 500 to 550 AH battery which pushes you into the 4 volt batteries so you would need 12 of something like a Rolls 4CS17PS battery.

Thank you for the heads up, I will research cost and availability of some of the batteries you suggested.

[Sunking]

I have yet to develop a battery plan, I was told to purchase enough deep cell 6 volt batteries to hook them together in series to develop a 24 volt system. I have a considerable supply of 6 volt 50 amp hour batteries and can renew them very cost efficient. Is this a bad idea?

Yep it is, sorry.

Here is the deal. With a 80 amp MPPTcharge controller the max panel wattage is roughly

1000 watts @ 12 volts
2000 watts @ 24 volts
4000 watts @ 48 volts

You have 2450 watts.

OK with 2450 watts will produce roughly 50 amps of charge current. The minimum size Flooded Lead Acid battery you can run with 50 amps of charge current is 400 Amp Hours. So for a 6 volt battery you are looking at 8 batteries something like a Trojan LR16RE-B or a Rolls S-530 battery.

Ideal size is a 500 to 550 AH battery which pushes you into the 4 volt batteries so you would need 12 of something like a Rolls 4CS17PS battery.

[paradiseisle]

Battery Plan

What battery voltage are you running? I assume 48 volts because at 2450 watts no one controller will work. At 48 volts will require a minimum 60 amp Model like Morning Star Tri-Star 60 Amp MPPT model. Bu tI suggest a 80 amp model so you can expand up to 4000 watts input if needed later on. Best is Outback FM80 and the very best is Mignight Solar 150 Classic.

No exactly, the hours of daylight have little to do with Sun Hours. Winter you are lucky to get 3 hours.

I have yet to develop a battery plan, I was told to purchase enough deep cell 6 volt batteries to hook them together in series to develop a 24 volt system. I have a considerable supply of 6 volt 50 amp hour batteries and can renew them very cost efficient. Is this a bad idea?

[Sunking]

Suggest a controller for my off grid system, (10) REC 245 watt panels

What battery voltage are you running? I assume 48 volts because at 2450 watts no one controller will work. At 48 volts will require a minimum 60 amp Model like Morning Star Tri-Star 60 Amp MPPT model. Bu tI suggest a 80 amp model so you can expand up to 4000 watts input if needed later on. Best is Outback FM80 and the very best is Mignight Solar 150 Classic.

My cabin is in the Sierra foothills at 3,000 feet, panels at full southern exposure, sun prevailing 6-8 hours daily year round.

No exactly, the hours of daylight have little to do with Sun Hours. Winter you are lucky to get 3 hours.

[paradiseisle]

Suggest a controller for my off grid system, (10) REC 245 watt panels, Thanks

Hi John,
I believe you and I are correct in most cases, unless you are talking about high latitude locations where it is very cool for substantial parts of the year. Then MPPT may be worth the cost. Although I am a bit wary of why an Outback 60 amp MPPT contoller costs twice as much as a Morningstar 60 Amp PWM controller and also that the Outback has two years warranty against the Morningstar's 5 year warranty. Is there something inherently less reliable about MPPT controllers? I would be interested in hearing about people's experience with MPPT controllers.

Jason the moderator has asked me to start a new thread, since this charge controller thing is only slightly related to LiFePo batteries. So I will do that by posting my original piece about the difference between charge controllers and the economics of their use. Derek disagreed with me which is fine because what we should all care about here is not who is right but what is factually correct. Without facts, we can make expensive errors and then people can say, See? I told you solar doesn't work! Gr-r-r!! that gets me mad since I have been living off-grid with all the amenities for decades and never had a power outage or burned out a light bulb, so I know it is superior to grid power.

Suggest a controller for my off grid system, (10) REC 245 watt panels, Thanks Paradise Isle, My cabin is in the Sierra foothills at 3,000 feet, panels at full southern exposure, sun prevailing 6-8 hours daily year round.

[Sunking]

Well you did not give the voltage or current so I assume 12 volt system running the full 30 amps will require #2 AWG to keep voltage drop to 2% or less.

[minijason9]

Solar system

The solar system is a wondrous creation filled with planets, moons, asteroids, comets and the sun. Study the solar system up close and personal by creating a model that demonstrates the differences in sizes of the plants and their distances from the sun. You'll learn more about the solar system after you make this solar system model mobile from simple items found in a hobby or craft store Mod note - forget the links

[Mike90250]

There is a great link to a spreadsheet caculator in my .sig

it was desigend just for solar PV and batteries.

stranded wire is mre flexible, solid belongs only in condouit so it cannot flex. (if it flexes much, it will break)

[joe shepherd]

I want to run the wire from the barn to the house. Its only a small system for a small fridge an maybe a few small things. I'mm gonna add on a little at a time.

[joe shepherd]

Thanks John,
Does it really matter if its hard wire or stranded?
I'm not using a converter either, so #8 would be the wire for my lights an small fridge?